GENETICS 8

CHROMOSOMAL DISORDERS

• It is caused due to absence or excess or abnormal arrangement of one or more chromosomes.

Change in number-

• Aneuploidy – failure of segregation of chromatids during cell division cycle results in the gain or loss of chromosome.
• Eg. 44A+ XY.  Normal male --- 44+XXY 
• Eg. 46 --- 47.      Trisomy
•        46----- 48.     Tetrasomy
•        46--- 45.     Monosomy
•         46---- 44.   Nullisomy

• Polyploidy – Failure of cytokinesis after telophase stage of cell division -- an increase in a whole set of chromosomes in an organism.

Eg.. normal diploid-- triploid

This condition is usually seen in plants.

• Down’s syndrome – gain of extra copy of chromosome 21 (trisomy 21)
• It was first described by Langdon Down (1866).
• Affected individual is short with small round head, furrowed tongue and partially open mouth.
• Broad palm with characteristic palm crease.
• Physical, psychomotor and mental development is retarded.

• Turner’s syndrome – loss of an X-chromosome in human females i.e. 45 with XO
• Such females are sterile as ovaries are rudimentary

• Klinefelter’s syndrome – presence of an additional copy of X-chromosome in male, resulting into karyotype, 47, XXY.
• Sterile individuals